Surface Area Of Electrode Material Research Articles

Effect of heat treatment temperature on electrochemical properties of organic silane microspheres

• The increase of temperature is conducive to the conductive network of carbon. • High temperature can improve the first coulombic efficiency of the material. • At a current density of 500 mA·g −1 , the specific capacity was 678.44 mAh·g −1 . Nano-SiO X (X ∼ 2.74) doped carbon composites were synthesized by simple co-condensation in Stöber waters and subsequent heat treatment, and the heat treatment process was studied. In the composites, carbon and silicon oxide are closely bonded. The doped carbon can provide continuous network to drop the specific resistance of the composites, to buffer volume effect of lithium embedding, so as to prevent the active substances from stripping from the collecting fluid. Higher heat treatment temperature reduces specific surface area of electrode materials, enhances the first charge-discharge capacity retention rate of the material, promotes the removal of carbon and oxygen elements, and improves the specific capacity of the material. After 100 cycles at 0.5 A·g −1 current density, the charge specific capacity was 678.44 mAh·g −1 . The composite provides excellent chemical properties, which makes it qualified to be an electrode composite for lithium-ion batteries.

Docked ions: Vertical-aligned tubular arrays for highly efficient capacitive deionization

Capacitive deionization (CDI) is an effective method for desalination of brackish water to alleviate the global freshwater crisis. Obtaining high desalination capacity is the primary focus of this field. Based on capacitive and pseudocapacitive behavior of the electrodes, current research is mainly devoted to increasing the specific surface area of electrode materials, however, the NaCl adsorption capacity is typically limited to the range of 10–20 mg g−1. In this work, we propose a new design paradigm of using a vertical-aligned nanotubular structure for CDI. This design allows ions to be temporarily held inside the electrodes like ships docked in a harbor (ion-docking effect, IDE) due to the greatly diminished water flow inside the tubes, thus enhancing the desalination capacity. As a result, the obtained CDI device based on vertical-aligned nanotubular P-TiO2 arrays shows an ultra-high NaCl adsorption capacity of ~60 mg g−1 within 30 min in 0.01 mol L−1 NaCl solution under 1.2 V, corresponding to a rapid average adsorption rate of 2 mg g−1 min−1. Moreover, the adsorption capacity could be further increased up to 121 and 136 mg g−1 under 1.2 and 1.5 V for 2.5 h adsorption, respectively, but still far from its equilibrium value. Finally, experiments and theoretical simulations are combined to further understand the IDE in CDI. This work highlights the discovery and the utilization of IDE in CDI, and provides new guidance for the design of CDI electrodes and can facilitate the development of CDI technology.

Hierarchical structure Ni3S2/Ni(OH)2 nanoarrays towards high-performance supercapacitors

The rational construction of the active materials with hierarchical structure is a feasible and effective strategy for realizing high electrochemical performance of supercapacitors. Herein, ultra-thin nickel hydroxide nanosheets are directly grow on the external surface of Ni3S2 nanorod arrays grew on nickel foam through simple hydrothermal ways to form Ni3S2/Ni(OH)2 hierarchical nanoarrays. The Ni3S2 nanorod arrays synthesized on nickel foam using hydrogen peroxide as an inducer could not only serve as the main channel for charge transport but also support the growth of active materials, moreover, the exposed active parts can also participate in the electrochemical energy storage process. The external ultra-thin nickel hydroxide nanosheets augment the contact region with the electrolyte and enrich the electrochemical active sites. The Ni3S2/Ni(OH)2 composite exhibits wonderful electrochemical performance is on account of its hierarchical structure could augment the effective specific surface area of electrode materials and induce a synergistic effect between each component. The aquaired Ni3S2/Ni(OH)2 electrode presents a brilliant specific capacitance (826 ​C ​g−1 during 1 ​A ​g−1) and relatively good rate performance (50% retention during 20 ​A ​g−1). In addition, our prepared hybrid supercapacitor used Ni3S2/Ni(OH)2 and AC acted as cathode and anode, respectively, gives rise to a superior energy density of 48.3 ​Wh kg−1 at about 800 ​W ​kg−1 of power density, together with retained about 70% capacitance after 10000 cycles at 5 ​A ​g−1. Meanwhile, two hybrid supercapacitor devices were fabricated in series to power a white LED, which can be continuously lit for more than 8 ​min.

Role of magnetism present in the cobaltites (ACo2O4 A = Co, Mn, and Fe) on the charge storage mechanism in aqueous supercapacitor

Recent reports on supercapacitor devices have shown that magnetic fields can alter the storage performance of these devices. To identify the origin of alteration of supercapacitive properties under magnetic field, recently, we have stressed upon the effect of the local environment of magnetised electrode material and proposed that two magnetic field-driven forces; Lorentz force and magnetic gradient force ∇F are active simultaneously in an electrochemical process. However, the impact of external magnetic fields on diffusive and/or capacitive storage of metal oxides is not known yet. Further, magnetism possessed by electrode material and its effect on the storage mechanism under magnetic field is also not explored yet. Here, we have found that the magnetic field contributes to double-layer capacitive storage and largely depends upon the magnetic features of electrode material. It is also observed that the surface area of electrode material does not contribute to total capacitance under the magnetic field. Based on the results, electrolyte’s convection due to Lorentz force induced by the magnetic field and thereby its effect on improving the capacitive storage is ruled out. Further, we have also shown that the local magnetic environment under magnetic field is crucial for any change in the supercapacitive properties.

Hierarchical porous CoFe2O4/CoFe2Se4 nanosheet as supercapacitor electrodes: Effect of selenium content and pore structure on electrochemical performance

Improving electrode conductivity and increasing electrode specific surface area are two strategies to enhance the storage performance of supercapacitors. Generally, to improve the conductivity of the electrode, a conductive polymer is usually coated on electrode. Nevertheless, polymer covers the pore structure, thus reduce the specific surface area of electrode material, which is not conducive to electrolyte contact and electron transfer. Therefore, the selenide nanosheet layer can be precipitated from the outer layer of CoFe2O4 nanosheet by means of selenation reaction, which can not only increase conductivity of electrode, but also increase the specific surface area of electrode, which can kill two things with one stone. So, the as-prepared CoFe2O4/CoFe2Se4 porous nanosheet electrode as the positive electrode shows an outstanding specific capacity of 933.6 C g−1 (1 A g−1). The device operating voltage of an aqueous asymmetric supercapacitor is 1.6 V, the energy density is 112.2 Wh kg−1 (power density of 400 W kg−1). The aqueous asymmetric supercapacitor has good cycle life, after 4000 cycles the capacity retention is 92.1%. Based on the discussion of charging time and charging current of mechanical energy charging supercapacitor, a satisfactory result is obtained, which is beneficial to the collection and utilization of mechanical energy in practical application.

Nanoporous RuO2 characterized by RuO(OH)2 surface phase as an efficient bifunctional catalyst for overall water splitting in alkaline solution

Abstract With the demand of renewable hydrogen energy, electrocatalytic water splitting is considered as the most promising method for hydrogen production. Herein, a simple synthesis of the nanoporous RuO2 (NP-RuO2) characterized by RuO(OH)2 surface phase was reported. The physical characterization of the materials are achieved by transmission electron microscope (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and X-ray photoelectron spectrometer (XPS). For HER activity, the NP-RuO2–450 electrode only needs 87 mV overpotential to obtain a current density of 10 mA cm−2, while RuO2 generates the same current density at a relatively large overpotential (η = 142 mV). Notably, the HER activity of NP-RuO2–450 is also higher than that of Pt (10 mA cm−2, η = 103 mV). The specific activity of NP-RuO2–450 is still 2.4 times higher than that of RuO2 reflecting the enhancement of the intrinsic activity. The OER activity of NP-RuO2–450 electrode has outperformed that of RuO2. The apparent activity of NP-RuO2–450 is 3.5 times that of RuO2 at an overpotential of 270 mV. For the specific activity, NP-RuO2–450 is still 1.9 times higher than that of RuO2. Therefore, NP-RuO2–450 electrode could be used as a bifunctional catalyst for overall water splitting. The excellent HER and OER activities of the NP-RuO2–450 electrode could be attributed to the enhancement of electrochemical surface area of electrode material. However, the more important reason is that the new surface phase creation of hydroxides and the electronic structure modification of Ru.

(Invited) Demystifying the Electrode/Electrolyte Interface in Carbon-Based Electrochemical Capacitors with Specs Technique and Electrochemical Dilatometry

It is often said that the highly developed surface area of electrode materials ensures high capacitance, power and energy in electrochemical capacitors. However, the real ‘efficiency’ of the surface exploited in charge storage remains unknown. Recently, it turned out that the Step Potential Electrochemical Spectroscopy (SPECS) technique can be a useful tool for determining it.The SPECS technique allows for the comprehensive analysis of the total current output and evaluation of the capacitive, redox and other components. Together with the physicochemical data from nitrogen and CO2 adsorption techniques, we aim at the determination of the real electrode/electrolyte interface surface.Based on the knowledge gained to date, we assume that the efficiency of the interface ‘exploitation’ depends on many factors: pore size distribution, wettability of the electrode material by electrolyte, as well as the size of the ions. Thus, inappropriate selection of one of these parameters can aggravate the device performance, even if the excellent carbon material is applied as electrode component.The paper will provide the results from SPECS correlated with the physicochemical properties of carbon materials. It appears that the electrochemically accessible surface does not exceed 30% of the values estimated by N2 or CO2adsorption. The results will be supported by the recent findings from electrochemical dilatometry experiments.

Mixed-dimensional heterostructure of few-layer MXene based vertical aligned MoS2 nanosheets for enhanced supercapacitor performance

Herein, a mixed-dimensional heterostructure of MoS2 deposited few-layer Ti3C2Tx nanosheets was synthesized to enhance the supercapacitor performance of pristine 2H phase MoS2 and Ti3C2Tx MXene. Through a facile hydrothermal method, with the introduction of MXene, MoS2 vertically aligns on the surface of few-layer Ti3C2Tx nanosheets and forms an interconnected network structure, which helps to increase the specific surface area of electrode material and improve the accessibility of electrolyte. Meanwhile, metallic Ti3C2Tx nanosheets serve as a highly conductive and stable matrix for MoS2 to grow on, incredibly accelerate the electron transfer and alleviate the aggregation of 2H–MoS2, thus bringing with an electrochemical performance improvement. The MoS2–Ti3C2Tx heterostructure shows a great enhancement in supercapacitor performance, which delivers a remarkable specific capacitance of 303.8 F g−1 at the current density of 1 A g−1, about 5 times of 2H phase MoS2 (62.8 F g−1) and 3 times of Ti3C2Tx (105.8 F g−1). Meanwhile, MoS2–Ti3C2Tx heterostructure electrode exhibits excellent cycling stability, which achieves a high capacitance retention up to 82% even after 10,000 cycles. After being assembled to a symmetric supercapacitor, a specific capacitance of 115.2 F g−1 at 0.5 A g−1 was achieved with good Coulombic efficiency (over 90%) and cycling stability (72.3% of capacitance retention after 10,000 cycles). Meanwhile, MoS2–Ti3C2Tx exhibits a high energy density of 5.1 Wh kg−1 at power density of 298 W kg−1, showing excellent SC performance. This study can provide an archetype of constructing mixed-dimensional heterostructure for synergistically integrating the advantages of different materials and enhancing the electrochemical performance.

Superbat: battery-like supercapacitor utilized by graphene foam and zinc oxide (ZnO) electrodes induced by structural defects.

The current work presents a hybrid type of energy storage device composed of both graphene foam and zinc oxide electrodes, which exhibits both the electrochemical performance of a supercapacitor with a relatively higher power density, and a battery with a relatively higher energy density as compared to each individual component as single devices. Te hybrid's improved performance was correlated to the defective structure of the electrodes. To enhance the electrochemical performance of supercapacitors, it is necessary to have a well-defined mass, shape, and surface area of electrode materials. Here, we present an original design of a mounting device that enabled precisely determining all the critical parameters of electrode materials for a particular mass and surface area. With the aid of our original setup, we produced a supercapacitor device that could also act as a battery due to its high energy density values, hence we named it as superbat. In this work, 3D graphene foam was used as the first electrode due to its large surface, while for the second electrode, ZnO nanocrystals were used due its defective structure. Paramagnetic resonance Raman and impedance spectroscopy were performed in order to understand the origin of the performance of the hybrid capacitor in more depth. In particular, we obtained a high specific capacitance value (C = 448 F g−1), which was exceptionally related not only to the quality of the synthesis but also the choice of electrode and electrolyte materials. Moreover, each component used in the construction of the hybrid supercapacitor also played a key role in to achieving high capacitance value. The results demonstrated the remarkable performance and stability of the superbat.

Enhancing the Electrochemical Performance of Electric Double-Layer Capacitors by Applying Mesoporous Carbon Gel RFCX to the Electrode

Electric double-layer capacitor (EDLC) has been required high capacitance and high-rate performance. The capacitance of EDLC comes from the electrostatic charge accumulation at the interface between electrode and electrolyte. So the capacitance is highly dependent on the surface area of elecrode material. For this reason, microporous activated carbon had been used for many years as EDLC electrode materials. However, recent research use organic electrolyte to enhance the energy density of EDLC. In this case, microporous electrode materials are not good at ion transport and reduce rate perfermance because of the large ion diameter of organic electrolyte. Therefore, an optimal electrode material must provide an appropriate pore size for ion transport. Recently, mesoporous materials have been reported to be more effective in increasing capacitance at high charge/discharge rates. Based on the recent reports, we focused on the study of novel mesoporous materials. We prepared several kinds of mesoporous materials carbon gel RFCX (resorcinol formaldehyde carbon xerogel) with different pore size distribution. RFCX is a kind of mesoporous carbon material with a 3D interconnected network structure and under the control of the pore structure by varying certain conditions of the sol-gel process. We controled the concentration of catalyst and developed three types of mesoporous materials carbon gel RFCX with a large number of mesopores around 10 nm, 25 nm and 40 nm. For comparison, we used two kinds of commercial activated carbon products M (surface area 900 m2g-1) and Y (surface area 1500 m2g-1). Both of them are high-surface-area microporous activated carbon. And we examined each sample’s electrochemical behavior as the electrode for electric double-layer capacitors in organic electrolyte of tetra ethyl ammonium tetra fluoroborate in propylene carbonate (TEABF4/PC). Ion diameter of electrolyte ion TEA+ in solvation is 1.96 nm. And ion diameter of electrolyte ion BF4 - in solvation is 1.71 nm. Diameter was caculated by Car-Parrinello method. Carbon gel RFCX enhanced the electrolyte ion transport by the large pore diameter (2 ~ 50 nm). RFCXs showed higher surface areal capacitance of 4.0 ~ 6.2 μF cm−2 than the commercial product M (0.5 ~1.5 μF cm−2) in organic electrolyte. Though they are the similar surface area (about 800 m2g-1 and 900 m2g-1). Moreover, the RFCXs also showed higher surface areal capacitance than the commercial product Y (2.2 ~ 3.5 μF cm−2). Though surface area of RFCX is only a half of Y (1500 m2g-1). And RFCXs showed high-rate performance of 70% owing to the large mesopore volume. These results indicated that capacitance of EDLC in organic electrolyte indepandent of surface area of electrode material. Thus, we considered that the volume rate of mesopore of electrode material is one of the most important determinant of rate performance. In summary, EDLC based on the mesoporous carbon RFCX exhibited better electrochemical performance than microporous activated carbon in organic electrolyte. It is considered that RFCX has potential for high performance energy-related applications.

High and rapid alkali cation storage in ultramicroporous carbonaceous materials

To achieve better supercapacitor performance, efforts have focused on increasing the specific surface area of electrode materials to obtain higher energy and power density. The control of pores in these materials is one of the most effective ways to increase the surface area. However, when the size of pores decreases to a sub-nanometer regime, it becomes difficult to apply the conventional parallel-plate capacitor model because the charge separation distance (d-value) of the electrical double layer has a similar length scale. In this study, ultramicroporous carbonaceous materials (UCMs) containing sub-nanometer-scale pores are fabricated using a simple in situ carbonization/activation of cellulose-based compounds containing potassium. The results show that alkali cations act as charge carriers in the ultramicropores (<0.7 nm), and these materials can deliver high capacitances of ∼300 F g−1 at 0.5 A g−1 and 130 F g−1, even at a high current rate of 65 A g−1 in an aqueous medium. In addition, the UCM-based symmetric supercapacitors are stable over 10,000 cycles and have a high energy and power densities of 8.4 Wh kg−1 and 15,000 W kg−1, respectively. This study provides a better understanding of the effects of ultramicropores in alkali cation storage.

Capacitance behavior of nanostructured ϵ-MnO2/C composite electrode using different carbons matrix

In this work nanostructured ϵ-MnO2/C composite electrode was synthesized via the reduction reaction of potassium permanganate. A wide range of carbons such as mesoporous carbon (MC), graphite (GC), super P carbon (super P) and Vulcan carbon (VC) were used in order to enhance the interfacial electrical conductivity and the electrochemical capacitance of the composite electrodes. Physical properties, structure and specific surface area of electrode materials were investigated by scanning electron microscopy (SEM), x-ray diffraction and nitrogen adsorption measurements. The capacitance behavior of MnO2/C materials was studied in aqueous and non-aqueous solution using cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements. The composite electrode exhibits the highest capacitance at 30 wt% activated carbon. Among different carbons used, the maximum capacitance of MnO2/super P electrode is as high as 205 F g−1 at 50 mV s−1 and retains 98% after 300 cycles.

Carbon/ λ-MnO 2 composites for supercapacitor electrodes

In the present work a composite of carbon with λ-MnO 2 have been synthesized by a simple two-step route. In the first step, to obtain LiMn 2O 4/carbon material, mesoporous activated carbon was impregnated with the solution of precursor metal salts and heated subsequently. As-prepared materials were acid treated which resulted in the formation of λ-MnO 2/carbon. Physical properties, structure and specific surface area of electrode materials were studied by TEM, X-ray diffraction and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. TEM images confirmed well dispersed λ-MnO 2 particles on the surface of carbon material. The carbon in the composite plays an important role as the surface area enhancing component and a support of pseudocapacitive material. Furthermore, the through-connected porosity serves as a continuous pathway for electrolyte transport. A synergetic effect of the porous carbon framework and of the redox properties of the λ-MnO 2 is at the origin of improvement of specific capacitance values which has been observed for composites after delithiation.

Hybrid materials for supercapacitor application

In the present study, a manganese oxide obtained by the acid treatment of LiMn2O4 spinel has been used as a positive electrode of supercapacitor. Removal of lithium from a spinel allowed to obtain MnO2 compound with the pores partly distributed in atomic scale, hence, an efficient use of its pseudocapacitive properties could be reached. On the other hand, residual lithium remaining in the structure preserved layered framework of MnO2 with pathways for ions sorption. Physical properties, morphology, and specific surface area of electrode materials were studied by scanning and transmission electron microscopy, and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge, and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. Neutral Li2SO4 aqueous solution has been selected for electrolytic medium. Extension of operating voltage for supercapacitor has been realized through asymmetric configuration with an activated carbon as a negative electrode. The asymmetric capacitor was operating within a voltage range up to 2.5 V (limited to 2.0 V for cycling tests) and was able to deliver a specific capacitance of 60 Fg−1 per capacitor at 100 mA g−1 current density. High specific energy of 36 Wh kg−1 was reached but with a moderate power density.

Charge storage mechanism of nanostructured anhydrous and hydrous ruthenium-based oxides

The charge storage mechanism of nanostructured anhydrous and hydrous ruthenium-based oxides was evaluated by various electrochemical techniques (cyclic voltammety, hydrodynamic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy). The effects of various factors, such as particle size, hydrous state, and structure, on the pseudocapacitive property were characterized. The electric double layer capacitance ( C dl), adsorption related charge ( C ad), and the irreversible redox related charge ( C irr) per unit mass and surface area of electrode material has been estimated and the role of structural water within the material either in micropores or interlayer are discussed.

Li + Storage Sites in Amorphous V 2 O 5 Prepared by Precipitation Method

Amorphous vanadium oxide powders were prepared by acidifying aqueous solution with concentrated nitric acid. Samples having a different degree of layer stacking and surface area were obtained either by changing the concentration or by employing additional solvent exchange process. The pentane-exchanged precipitate gave the largest surface area after vacuum drying at 100°C for 24 h. This electrode material delivered an initial discharge capacity of in the voltage range of 1.5-4.0 V (vs. which amounts to 2.9 equiv ions per mol of X-ray absorption near-edge spectra (XANES) clearly showed a vanadium reduction down to V(III) when ions were inserted at The storage sites were analyzed by correlating the peak intensity in differential capacity plots to the surface area and degree of layer stacking, from which two different storage sites were identified. The discharging capacity at 1.7 V was strongly correlated with the surface area of electrode material, suggesting that ions are inserted into the amorphous region at this potential. The intensity of 2.5 V peak was, however, proportional to the peak intensity of (001) diffraction, illustrating that ions are inserted into the quasi-ordered layer stacking region at this potential. The latter feature was further confirmed by X-ray diffraction analysis, whereby it was found that the interlayer spacing decreases most significantly near 2.5 V along with a sharp decrease in the (001) diffraction intensity. © 2003 The Electrochemical Society. All rights reserved.

Photoelectrochemical properties of sol-gel and particulateTiO2layers

Polarization curves on irradiatedTiO2layers were measured in various electrolytes, namely sodium hydroxide, sulphuric acid, oxalic acid and potassium oxalate. Photocurrents measured in 0.1M NaOH are very small and decrease with increasing number of Degussa P25TiO2layers. Photocurrents for sol-gelTiO2layers in 0.1M NaOH are about five times higher than for P25TiO2layers and increasing with number of layers. The same holds forNa2SO4, but inH2SO4the difference between P25 and sol-gel diminishes, however the sol-gel layers still show the higher currents. In solutions of oxidizable substrates the trend is inversed: P25 layers show higher currents, with a steep increase with concentration of solute. The shape of the polarization curves was interpreted in terms of response time to irradiation and photocurrent depletion. Degradation experiments demonstrated that the effect (and advantage) of biasing the electrode depends on adsorption properties of substance and surface area of electrode material.